Sprint Corp. shares tumbled almost 7% Monday, as investors responded to the news that Japan's Softbank Group Corp. has agreed to acquire ARM Holdings in a $32 billion deal. Softbank acquired Sprint in 2013 and has struggled since then to turn the company around by cutting costs, offering discounts and working to upgrade its network. Today's deal is expected to divert attention from the fourth=biggest mobile carrier in the U.S., which has not made a profit in years. Softbank founder Masayoshi Son, speaking about Softbank's fiscal fourth-quarter earnings in May, declined to say when Sprint would likely return to profitability. Sprint shares have nonetheless gained about 29% in the year so far, outperforming the S&P 500 roughly 6% gain.